Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis are members of the Bacillus cereus group of bacteria, demonstrating widely different phenotypes and pathological effects. B. anthracis causes the acute fatal disease anthrax and is a potential biological weapon due to its high toxicity. B. thuringiensis produces intracellular protein crystals toxic to a wide number of insect larvae and is the most commonly used biological pesticide worldwide. B. cereus is a probably ubiquitous soil bacterium and an opportunistic pathogen that is a common cause of food poisoning. In contrast to the differences in phenotypes, we show by multilocus enzyme electrophoresis and by sequence analysis of nine chromosomal genes that B. anthracis should be considered a lineage of B. cereus. This determination is not only a formal matter of taxonomy but may also have consequences with respect to virulence and the potential of horizontal gene transfer within the B. cereus group.

Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis—One Species on the Basis of Genetic Evidence

Although homologous recombination and DNA repair phenomena in bacteria were initially extensively studied without regard to any relationship between the two, it is now appreciated that DNA repair and homologous recombination are related through DNA replication. In Escherichia coli, two-strand DNA damage, generated mostly during replication on a template DNA containing one-strand damage, is repaired by recombination with a homologous intact duplex, usually the sister chromosome. The two major types of two-strand DNA lesions are channeled into two distinct pathways of recombinational repair: daughter-strand gaps are closed by the RecF pathway, while disintegrated replication forks are reestablished by the RecBCD pathway. The phage λ recombination system is simpler in that its major reaction is to link two double-stranded DNA ends by using overlapping homologous sequences. The remarkable progress in understanding the mechanisms of recombinational repair in E. coli over the last decade is due to the in vitro characterization of the activities of individual recombination proteins. Putting our knowledge about recombinational repair in the broader context of DNA replication will guide future experimentation.

Recombinational Repair of DNA Damage in Escherichia coli and Bacteriophage λ

It has been a decade since multicellularity was proposed as a general bacterial trait. Intercellular communication and multicellular coordination are now known to be widespread among prokaryotes and to affect multiple phenotypes. Many different classes of signaling molecules have been identified in both Gram-positive and Gram-negative species. Bacteria have sophisticated signal transduction networks for integrating intercellular signals with other information to make decisions about gene expression and cellular differentiation. Coordinated multicellular behavior can be observed in a variety of situations, including development of E. coli and B. subtilis colonies, swarming by Proteus and Serratia, and spatially organized interspecific metabolic cooperation in anaerobic bioreactor granules. Bacteria benefit from multicellular cooperation by using cellular division of labor, accessing resources that cannot effectively be utilized by single cells, collectively defending against antagonists, and optimizing population survival by differentiating into distinct cell types.

Thinking about bacterial populations as multicellular organisms

Nitroaromatic compounds are released into the biosphere almost exclusively from anthropogenic sources. Some compounds are produced by incomplete combustion of fossil fuels; others are used as synthetic intermediates, dyes, pesticides, and explosives. Recent research revealed a number of microbial systems capable of transforming or biodegrading nitroaromatic compounds. Anaerobic bacteria can reduce the nitro group via nitroso and hydroxylamino intermediates to the corresponding amines. Isolates of Desulfovibrio spp. can use nitroaromatic compounds as their source of nitrogen. They can also reduce 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene. Several strains of Clostridium can catalyze a similar reduction and also seem to be able to degrade the molecule to small aliphatic acids. Anaerobic systems have been demonstrated to destroy munitions and pesticides in soil. Fungi can extensively degrade or mineralize a variety of nitroaromatic compounds. For example, Phanerochaete chrysosporium mineralizes 2,4-dinitrotoluene and 2,4,6-trinitrotoluene and shows promise as the basis for bioremediation strategies. The anaerobic bacteria and the fungi mentioned above mostly transform nitroaromatic compounds via fortuitous reactions. In contrast, a number of nitroaromatic compounds can serve as growth substrates for aerobic bacteria. Removal or productive metabolism of nitro groups can be accomplished by four different strategies. (a) Some bacteria can reduce the aromatic ring of dinitro and trinitro compounds by the addition of a hydride ion to form a hydride-Meisenheimer complex, which subsequently rearomatizes with the elimination of nitrite. (b) Monooxygenase enzymes can add a single oxygen atom and eliminate the nitro group from nitrophenols. (c) Dioxygenase enzymes can insert two hydroxyl groups into the aromatic ring and precipitate the spontaneous elimination of the nitro group from a variety of nitroaromatic compounds. (d) Reduction of the nitro group to the corresponding hydroxylamine is the initial reaction in the productive metabolism of nitrobenzene, 4-nitrotoluene, and 4-nitrobenzoate. The hydroxylamines undergo enzyme-catalyzed rearrangements to hydroxylated compounds that are substrates for ring-fission reactions. Potential applications of the above reactions include not only the biodegradation of environmental contaminants, but also biocatalysis and synthesis of valuable organic molecules.

Biodegradation of Nitroaromatic Compounds

A fellow of my acquaintance, on seeing a colleague drink undiluted water (55.5 molal), has been known to comment in disapproval that water at such a concentration should not be used for that purpose and that its main function is for putting around the outside of boats. He conceded that dilution with a little salt is acceptable for boats but for no other purpose. The proponent of this philosophy is not a biologist and it is unlikely that many biologists would accept his generalization without some qualification. Nevertheless, it is a point of view. Another point of view with which all biologists might not agree, at least initially, is one which I wish to advance in this review. It is that, notwithstanding the indispensability of water in living systems and the unique properties of solvent water, quantitative variations in the amount of water available are of less direct microbiological significance than is generally conceded.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1991&context=smhpapers

Microbial water stress.

Enzymatic oxidation of p-nitrophenol

The Role of Peroxide in the Biological Effects of Irradiated Broth.

The fine structure of Azotobacter vinelandii has been studied by means of electron microscopy of ultrathin sections made of the encysting and germinating cells. The organisms were fixed with KMnO4 and embedded in epoxy resin. On an encystment medium the rod-shaped bacteria begin to assume an almost spherical form and then bark-like exine appears in 1½ to 2 days. The exine thickens and an electron permeable intine forms between it and the shrinking cell body. In 5 days the intine makes up more than half of the cyst volume and begins to show a definite two-layered structure. Meanwhile the peripheral bodies, which may be extensions of the cell membrane of the vegetative cell, disappear as the encystment progresses. The cell wall and membrane of the vegetative cell remain demonstrable as the confining structure of the shrinking central body of the mature cyst. In this central body lipoidal globules appear together with aggregations of nuclear material. Cyst germination begins with an increase in the size of the central body at the expense of the intine. The nuclear aggregations become more diffuse and the lipoidal globules disappear. The exine may be pushed outward and the bark-like fragments separate as the emerging vegetative cell develops. Invagination of the cell wall and membrane may occur at this stage leading to cell division. Empty exines remain as horseshoe-shaped structures.

https://rupress.org/jcb/article-pdf/10/4/555/1050941/555.pdf

Development and germination of the Azotobacter cyst.

A saline pond in a region in Antarctia where other lakes and ponds are frozen remains unfrozen at the prevailing low temperatures. The ecology of the pond is unique. A distinctive aerobic microbial population, though restricted to this natural habitat, adapts to growth in artificial culture. The growth habit of these organisms, as seen in nature and in laboratory culture, indicates a possible relationship between growth at high salt concentration, at low temperatures, and in media of low organic content.

Antarctica: The Microbiology of an Unfrozen Saline Pond.

Socolofsky, M. D. (University of Texas, Austin) and Orville Wyss. Resistance of the Azotobacter cyst. J. Bacteriol. 84: 119–124. 1962—The Azotobacter cysts were found to be more resistant than the vegetative cells to various harmful agents. Studies involving ultraviolet irradiation indicated that cysts required twice as great a dosage, as correspondingly treated vegetative cells, to be 90% inactivated. The acquisition of ultraviolet resistance during the encystment process was gradual and appeared to be related to the formation of exine and intine. A slow loss of ultraviolet resistance during germination was also noted. The cysts exhibited no marked resistance to heat, although they were extremely resistant to gamma radiation, sonic treatment, and desiccation. Evidence was presented indicating that the cyst is not a bacterial endospore. The encystment process may confer a survival advantage upon the organism by coupling the low endogenous respiration rate with the ability to withstand desiccation. Images

Orville Wyss

Papers

Enzymatic oxidation of p-nitrophenol

The Role of Peroxide in the Biological Effects of Irradiated Broth.

Development and germination of the Azotobacter cyst.

Antarctica: The Microbiology of an Unfrozen Saline Pond.

Resistance of the azotobacter cyst